Transducer device for electrically operated brakes

ABSTRACT

An electro-mechanical pressure responsive control system and apparatus for controlling the current supplied to the actuating coils of electric brakes of a towed vehicle. The control includes a transducer having a flexible bellows with a powdered magnetic material received therein which, when compressed by foreshortening of the bellows due to operation of the brake system of a towing vehicle, decreases in electrical resistance and thereby supplies greater current to the brakes of the towed vehicle, and vice versa. A magnetic field prevents the powdered material from becoming permanently compacted by repeated cycling of the bellows.

United States Patent 91 Hubbard [451 July 16', 1974 TRANSDUCER DEVICEFOR 3,350,142 l0/l967 Schuman....- 303/7 ELECTRIC ALLY OPERATED BRAKES3,486,799. 12/ 1969 Greentree 303/7 [75] Inventor: Harold C. Hubbard,Lansing, Mich. Primary Examiner Duane Reger [73] Assignee: Motor WheelCorporation, Lansing, Assistant Examiner-D Butler Mi h Attorney, Agent,or Firm-Barnes, Kisselle, Raisch & 22 Filed: Jan. 12, 1973 Chate [21]Appi. NO.: 322,946 [57] ABSTRACT An electro-mechanical pressureresponsive control 52 us. c1. 303/7, 73/398 AR 303/15 System andapparatus for commlling the current P- 338/101 plied to the actuatingcoils of electric brakes of a 51 Int. Cl B60t 13/66 Owed vehicle Theincludes a transducer [58] Field of Search 303/7 3 2 15 13, 20 ing aflexible bellows with a powdered magnetic mate- 303/16 188/3 158 36 rialreceived therein which, when compressed by fore- 1014,13 4 shortening ofthe bellows due to operation of the brake system of a towing vehicle,decreases in electri- 56 I R d cal resistance and thereby suppliesgreater current to 1 e erences the brakes of the towed vehicle, and viceversa. A

UNITED STATES PATENTS magnetic'field prevents the powdered material from2 genardos becoming permanently compacted by repeated cycling enrose3,212,065 10/1965 Leonard... 188/158 Ofthe bellows 3,283,283 1 H1966Denner et al. 338/41 13 Claims, 3 Drawing Figures M345 7E1? TOW/N5VEH/CLE CYL/NDER BRA/(E3 3% 0 Zfi a ZZ i- T/PA/VSDUCEF 9 6/ 45 HA/VDCONTROL This invention relates to a control System for electricallyoperated brakes of a towed vehicle and more particularly to anelectro-mechanical rheostat or transducer for controlling the currentsupplied to the brakes of the towed vehicle in proportion to the forceapplied to the brakes of the towing vehicle.

It is customary today to provide certain types of towed vehicles, suchas house trailers, travel trailers, campers and boat trailers, withelectrically-actuated brakes of the type disclosed in US. Pat. No.3,244,259 and to operate such brakes from the electrical system of thetowing vehicle. Various electric brake control systems have beenprovided for manual operation by the driver of the towing vehicle, suchas wiper and leaf switch type rheostat controls mounted on .the steeringcolumn or dashboard of the towing vehicle or preferably electroniccontrollers such as disclosed in US. Pat. No. 3,503,652. Also, slaveelectric brake control systems have been provided, alone or inconjunction with such manual controls, which are controlled in relationto or responsive to actuation of the tractor or towing vehicle brakepedal, either directly by mechanical coupling to the foot pedal orindirectly in response to the fluid pressure developed upon applicationof the brakes of a hydraulic or pneumatic brake system of the towing ortractor vehicle. Various forms of transducer devices have been proposedin such control systems for sensing the mechanical force applied to thetractor brakes or fluid pressure developed in response thereto to causethe operating current in the electric system which is applied to thebrake-operating magnets in the electric braking system to varyapproximately in proportion to the force applied to and/or pressuredeveloped in the hydraulic system. One such form of transducer is thatdisclosed in US. Pat. No. 2,454,291 wherein a carbonpilecompression-rheostat is proposed in which the flow of current iscontrolled by varying the pressure on a pile or stack of resistor discsor elements which may be made of carbon or similar material. Anotherform of pressure variable resistor is that shown in U.S. Pat. No.3,574,414. However, such force or pressure sensing transducers eitherlack reliability, are too costly, or are incapable of operating as aseries element in the load circuit and therefore require electronicamplifying circuitry to isolate the sensor from the load circuit.

Accordingly, it is an object of the present invention to provide atrailer braking control system which is safe, reliable and compatablewith existing types of trailer electric brakes, which is capable ofcontrolling trailer braking forces proportional to tractor brakingforce,'which can be either mechanically actuated by the foot pedal ofthe towing vehicle or by the fluid pressure developed in the fluidbraking system of the towing vehicle, and which incorporates an improvedpressure responsive variable resistance device which requires a minimumdisplacement and thus minimizes the volume of fluid withdrawn from thehydraulic system to 7 description, appended claims and accompanyingdrawings in which:

FIG. 1 is a schematic view of the hydraulic and elecv pedal of a towingvehicle- Referring to the drawings in more detail, FIG. I schematicallyillustrates a hydraulic brake system of a towing vehicle having a brakepedal 10 mechanically connected by the usual linkage to a mastercylinder 12 which is coupled through brake fluid lines 14 to wheel brakecylinders 16. A variable rheostat device 18, herein termed a transducer,and embodying this invention is connected with master cylinder 12 by abranch fluid line 20 communicating with the pressure fluid in line 14. Abattery 22 in the towing vehicle, which may be theusual 12-volt ignitionand illumination storage battery of the vehicle, supplies direct currentto transducer 18 and to a conventional hand control 24 to energize andcontrol the electromagnetic brake coils 26 and 28 of the conventionalelectric brake system of a towed vehicle such as a trailer. Transducer18 has one terminal thereof connected by a lead 30 to one terminal of anormally open switch 32, such as a stoplight switch operated by mastercylinder 12, which in turn has its other terminal connected by a lead 34to the positive terminal of battery 22. The other terminal of transducer18 is electrically connected with parallel brake coils 26 and 28 by lead36 and parallel branch leads 38, the opposite ends of the coils beingconnected to chassis ground. Hand controller 24 is connected in shuntwith transducer 18 between coils 26 and 28 and battery 22 via leads 38and 40.

As shown in FIG. 2, transducer 18 has a generally rectangular metallicframe or housing 42 with a bellows assembly 44 received therein. Bellowsassembly 44 is actuated by the plunger of a hydraulic cylinder 46 whichextends through and is stationarily mounted in one end of frame 18 andwhich is connected with master cylinder 12 through hydraulic line 20.Bellows assembly 44 has-two generallyopposed circular hatshaped end caps48 and 48 with a plurality of axially spaced washers 50 interposedbetween the ends caps, the caps and washers being made of a heatconductive paramagnetic material such as aluminum. A ring 52 of aflexible resilient electrically nonconductive material, such as asilicone rubber adhesive such as that sold under the trademark SILASTICby General Electric Company, is interposed between and bonded to thefaces of each adjacent pair of washers 50 and end caps 48. Washers 50preferably extend radially inwardly and outwardly beyond resilient rings52 to provide heat transfer cooling fins for bellows assembly 44.

Each end cap 48, 48 has a cup 54, 54' with an axially polarized ceramicdisc permanent magnet 56, 56' received therein. Preferably, magnets 56,56 are oriented coaxially and so that the north pole of one disc magnetfaces the south pole of the other disc magnet. Bellows assembly 44 ispartially filled with a powdered magnetic material 58, such as powderednickel, pow- 3 dered iron or a mixture thereof. if desired, bellowsassembly 44 can be evacuated and then injected with an .inert gas suchas nitrogen to prevent oxidation of the powdered magnetic material. Leadwires 34 and 36 are FIG. 3 illustrates a modified form of a transducerdevice 18, also in accordance with the present invention, which ismounted on a fire wall 66 of a towing vehicle and mechanically connectedwith a swing arm 68 of a brake pedal of the towing vehicle. A bellowsassembly 70 of transducer device 18' is connected to arm 68 through thearm 71 of a bracket 74 fixed by screws 73 to an actuating rod 72 of ahydraulic master cylinder (not shown, but which may be, the same asmaster cylinder 12 with brakelight switch 32) of the brake system of thetowing vehicle. Rod 72 is connected to arm 68 by a pivot pin 75 retainedon the arm by a nut 76. Bellows assembly 70 is yieldably connected toarm 71 by a spring 78 having one end thereof received in a cup 80 fixedto the arm and the other end received over the shank of a retainer 82.Bellows assembly 70 is generally I similar to bellows assembly 44 andhas a pair of circular opposed electrically conductive end caps 84, 84and a plurality. of washers 86, both of, a paramagnetic material, suchas aluminum, received in a tubular cover 88 made of a flexible resilientrubber material and bonded thereto by a suitable epoxy adhesivematerial. A pair of ceramic disc magnets 56 and 56 are received one ineach end cap 84, 84' and the end caps are adhered to nylon electricalinsulators 90.and 92 by a suitable adhesive. Insulator 90 has aprojection 94 thereon received in a hole in tire wall 66 and insulator92 is threadably connected to a stud of spring retainer 82. Leads 34 and36 are each electrically connected to one of the end caps 84.. Bellowsassembly 70 thus is located in a protected area between brake pedal arm68, fire wall 66 and'th'e steering column 96 of the towing vehicle.

In operation, when the towing vehicle brakes are applied by depressingthe brake foot pedal, bellows assembly 44 or 70 of transducer device 18or 18' is partially collapsed or foreshortened. With respect to thefirst form-of transducer 18, bellows 44 is foreshortened by theextension of plunger 62 of hydraulic cylinder 46 in proportion to thefluid pressure created by master cylinder 12 as it is actuated by footpedal 10. With respect to the modified transducer 18', bellows assembly70 is foreshortened due to arm 68 pivoting clockwise and thus moving rod72 and arm 71 toward the fire wall 66, this action occurring inproportion to the displacement of arm 68 which in turn .is displaced inproportion to the force applied thereto by the operator. Hence, in bothtransducer devices 18 and 18', the bellows assembly 44 or 70 isforeshortened in proportion to the braking force applied to thehydraulic brake system .of the towing vehicle by the operator thereof.

' --lnitial actuation of the master cylinder 12 closes brakelight switch32 to supply current from battery 22 to transducer 18 or 18 throughleads 34 and 30. The aluminum end caps 48 or 84 each provide oneterminal of the transducer devicethrough which current flows frombattery 22 in proportion to the resistance offered by the magneticpowdered material 58 received in the bellows assembly. The electricalresistance of powdered magnetic material 58 varies generally in directproportion to the compression force applied axially to the bellowsassembly. Hence, with the battery voltage being essentially constant, asthe powdered mixture is compressed, its electrical resistance decreasesand thus causes an increase in the current flow from battery 22 throughthe transducer device 18 or 18" to the electrical brake coils 26 and 28of the towed vehicle, resulting in the application of a braking force onthe towed vehicle proportional to the braking force developed in'the.towing vehicle. When bellows assemblies 44 and'70 are completely relaxedor extended, transducer devices 18 and 18' have a very high electricalresistance such that practically no current flows through thetransducers.

Moreover, when the bellows. assemblies are completely extended, switch30 is open and thus the towed vehicle brake-coils 26'andv 28 are notenergized.

In the absence of magnets 56, repeated foreshortening ofbellowsassemblies 44 and would tend to permanently compact and adhere theparticles of magnetic material 58 to each other so that transducer j 18or 18 would not provide a variable electrical resistance in proportionto the force applied thereto. nowever, in accordance with one principalfeatureof the invention, the magnetic lines of force provided by, andex-tendingaxially of the bellows chamber between the pair of discmagnets 56 and 5 6 tend to draw the powdered particles of magneticmaterial toward the magnets to'thereby loosen or break up any compactingor adhesionof the'particles resulting from foreshortening of the bellowsassemblies. Thus, due to the magnets, the powdered particles recoverwhen the bellows assemblies are'extended to their relaxed ornormallength after each pressure application so that they can again achieve ona repetitive basis their original design value of high electricalresistance provided by the loose, less compacted form of particledistribution in the bellows chamber. The bellows are expanded to theirnormal relaxed length whenever the .brakesof the towing vehicle are notactuated, either due to the resiliency of rings 5-2 in assembly 18 ordue to the combinedaction of resilient cover 88 and spring 78 inassembly 18. If desired, permanent magnets 56, 56 can be replaced withor augmented by a coil of electrically conductive material such as wirewound around the exterior of the bellows assemblies and electricallyconnected to the brake control circuit to provide an electromagnethaving a field when energized extending axially of the bellows chamber.

From the foregoing description, it will-now be evident that the ruggedconstruction of the transducer devices 18 and 18' of this invention andthe use of a magnetic field to prevent the compacting of the powderedmaterial by repeated cycling of thebellowsassembly provides amaintenance and service free transducer control system and device with along useful life. The

netic material.

It will also be understood that, with respect to the first form ofbellows 18, the radial thickness of the resilient rings 52 may be variedto provide proper resiliency and compressibility characteristics for agiven application, taking into account the number and spacing of discs50. Moreover, the distance by which the inner edges 53of disc 52protrude radially inwardly from the inner periphery of the associatedrings 52 is a significant factor in determining the force required tocompress the powder 58 as well as the cooling effect provided by washers50. The farther the washers protrude into the powder, the more powderwhich will be trapped between the washers and thus the greater will bethe resistance offered to compression of the bellows.

vThus, if a low squeeze force is desired, the inner pevice versa for ahigh squeeze force. On the otherhand,

the farther the washers protrude into the powder, the better will be theheat transfer characteristics provided by the washers for conductingheat from the powder mass radially outwardly to the exterior of thebellows for dissipation by the radially outwardly protruding portions orfins of the washers.

It is to be further understood that either of the transducer devices 18or 18 can be coupled to a manual control through a suitable forcemultiplying mechanical linkage employing, for example, a Bowden wireextension to a dashboard mounted handle (somewhat similar to that shownin U.S. Pat. No. 3,497,266). In this way, compression force may bemanually applied to the bellows assembly 44 or 70 to thereby provide thetowing vehicle operator with a separate hand controlled means ofapplying the trailer brakes using the same control transducer 18 or 18.If the force applicator of the manual linkage is arranged similar toplunger 62 so as to have abutment contact with cap 60', and is suitablyspring retracted when handpres'sure is relieved from the manual control,the application of the towing vehicle brakes via the foot pedal willoverride the manual control and cause conjoint operation of the towingvehicle and trailer brakes.

Although the transducers 18 or 18 of the present invention haveparticularly desirable features in a trailer brake control system of thepresent invention, the transducers themselves also are advantageous inother applications in which a variable resistance circuit element isdesired which is responsive to pressure to vary the resistance of theelement, and in which large forces are encountered on a repetitive basisand a uniform recovery characteristic is desired over a prolonged cycleof life.

By way of illustration, and not by way of limitation,

one successful working embodiment of a transducer 18 constructed inaccordance with the present invention employed the followingstructuralspecifications:

Axial dimension from magnet 56 to magnet 1%" (HO. 2) 56' in the fullyrelaxed state Continued Axial distance between washers 52 in V4 relaxedstate Axial thickness of washers 52 1/32" Radial thickness of rings 52/z" Weight of charge of powder 58 contained in 36.322 grams bellowschamber Type. diameter and axial thickness of Ceramic "/1" ceramic discmagnets 56 and 56' Range offorce applied by plunger 62 die. 5 lbs. tomax. brake rod) pressure Range of resistance values provided by l ohm tol megohm transducer 18 Range of values of current flow through 0.000012amps min. 6 transducerl8 amps max. with 2 pucks load Average particlesize and composition of powder 58 Typical physical properties:

Apparent density 2.85 grams/cc Flow rate 26 seconds 7 Typical screenanalysis: On 60 U.S. Mesh 0% 60 +l0O'Mesh 2.0% l0,0 'Mesh 22.0% l40 +200Mesh 25.0% 200 +325 Mesh 28.0% -325 Mesh g 23.0% Typical chemicalanalysis: iron content 99+7 Hydrogen loss 0.18% Carbon 0.037: Sulphur0.0l5'/( Manganese 0.009% Phosphorous 0.02571 Silicon 0.09% Acidinsolubles 0.17%

lclaim:

l. A pressure responsive variable electrical resistance electric brakecontrol device comprising, a flexible bellows having a chamber thereinand capable of being contracted and expanded in a given direction inresponse to forces applied oppositely thereto generally in saidgiven-direction, a pair of electrically conductive contacts associatedwith said bellows disposed in spaced relation along said givendirection, a powdered magnetic material received in said bellows chamberbetween and in engagement with both of said electrically conductivecontacts, means providing a magnetic field having lines of magneticforce extending within said bellows chamber generally in said givendirection, and force application means adapted to foreshorten saidflexible bellows and thereby apply pressure to said powdered material inproportion to the force applied by an operator in actuating the brakesystem of a towing vehicle, whereby contraction of said bellows inresponse to said applied forces compresses said powdered magneticmaterial received in said bellows and thereby decreases the electricalresistance between said conductive contactsin proportion to the value ofthe applied forces.

. 2. The control device of claim 1 wherein said bellows is generallytubular with the axis thereof extending in said given direction, andwherein said force application means comprises a hydraulic cylindermounted in relation to said bellows to apply a generally axial forcethereto to foreshorten said bellows, said hydraulic cylinder beingadapted for fluid coupling with a master cylinder of a hydraulic brakesystem of a towing vehicle.

3. The control device of claim 1 in which said force application meanscomprises a brake pedal of a towing vehicle and resilient meansyieldably connecting said bellows with said pedal'for shortening saidbellows in proportion to the displacement of the brake pedal of the.towing vehicle during actuation thereof by the operation of the towingvehicle in applying the towing vehicle brakes.

4. The control device of claim I wherein said electrically conductivecontacts comprise a pair of generally opposed axially aligned end capsconnected to opposed ends of said flexible bellows, said end caps beingmade of an electrically conductive paramagnetic material.

5. The control device of claim 1 wherein said bellows comprises agenerally tubular enclosure defining a chamber therein receiving saidpowdered material therein and a plurality of washers of -a paramagneticmaterial generally axially spaced from one another and each at leastpartially received in said chamber.

6. The control device of claim 5 including a plurality of rings of aflexible resilient electrical insulating material interleaved with saidwashers and individually bonded to opposed faces of adjacent washerswith said washers extending generally radially outwardly beyond saidrings of flexible resilient material.

7. The control device of claim 6 wherein said flexible resilientmaterial of said rings is a silicone rubber.

8. The control device of claim 6 wherein said conductivec'ontactscomprise a pair of axially spaced gen- '8 erally'opposed endcaps each bonded to one of said rings of resilient flexible materialwith all of said washers interposed between said end caps.

9. The control device of claim 5 wherein said tubular enclosurecomprises a resilient flexible sleeve secured to the outer peripheriesof said washers.

10. The control device of claim 1 wherein said means providing amagnetic field comprises a'pair of permanent magnets spaced apart insaid chamber and mounted with their polar axes extending in said givendirection.

11. The control device of claim 10 wherein said per-' manent magnetscomprise axially polarized circular discs mounted in generally axiallyopposed relation adjacent opposite ends of said bellows chamber.

12. The control device of claim 11 wherein said magnets compriseceramicdisc magnets mounted in coaxiallyopposed relation adjacentopposite ends ofsaid flexible bellows.

13. The control device of claim 12 wherein said disc permanent magnetsare mounted one on each of said end caps in generally axially opposedrelation with the one pole of one of said magnets facing the oppositepole of the other of said magnets.

1. A pressure responsive variable electrical resistance electric brakecontrol device comprising, a flexible bellows having a chamber thereinand capable of being contracted and expanded in a given direction inresponse to forces applied oppositely thereto generally in said givendirection, a pair of electrically conductive contacts associated withsaid bellows disposed in spaced relation along said given direction, apowdered magnetic material received in said bellows chamber between andin engagement with both of said electrically conductive contacts, meansproviding a magnetic field having lines of magnetic force extendingwithin said bellows chamber generally in said given direction, and forceapplication means adapted to foreshorten said flexible bellows andthereby apply pressure to said powdered material in proportion to theforce applied by an operator in actuating the brake system of a towingvehicle, whereby contraction of said bellows in response to said appliedforces compresses said powdered magnetic material received in saidbellows and thereby decreases the electrical resistance between saidconductive contacts in proportion to the value of the applied forces. 2.The control device of claim 1 wherein said bellows is generally tubularwith the axis thereof extending in said given direction, and whereinsaid force application means comprises a hydraulic cylinder mounted inrelation to said bellows to apply a generally axial force thereto toforeshorten said bellows, said hydraulic cylinder being adapted forfluid coupling with a master cylinder of a hydraulic brake system of atowing vehicle.
 3. The control device of claim 1 in which said forceapplication means comprises a brake pedal of a towing vehicle andresilient means yieldably connecting said bellows with said pedal forshortening said bellows in proportion to the displacement of the brakepedal of the towing vehicle during actuation thereof by the operation ofthe towing vehicle in applying the towing vehicle brakes.
 4. The controldevice of claim 1 wherein said electrically conductive contacts comprisea pair of generally opposed axially aligned end caps connected toopposed ends of said flexible bellows, said end caps being made of anelectrically conductive paramagnetic material.
 5. The control device ofclaim 1 wherein said bellows comprises a generally tubular enclosuredefining a chamber therein receiving said powdered material therein anda plurality of washers of a paramagnetic material generally axiallyspaced from one another and each at least partially received in saidchamber.
 6. The control device of claim 5 including a plurality of ringsof a flexible resilient electrical insulating material interleaved withsaid washers and individually bonded to opposed faces of adjacentwashers with said washers extending generally radially outwardly beyondsaid rings of flexible resilient material.
 7. The control device ofclaim 6 wherein said flexible resilient material of said rings is asilicone rubber.
 8. The control device of claim 6 wherein saidconductive contacts comprise a pair of axially spaced generally opposedend caps each bonded to one of said rings of resilient flexible materialwith all of said washers interposed between said end caps.
 9. Thecontrol device of claim 5 wherein said tubular enclosure comprises aresilient flexible sleeve secured to the outer peripheries of saidwashers.
 10. The control device of claim 1 wherein said means providinga magnetic field comprises a pair of permanent magnets spaced apart insaid chamber and mounted with their polar axes extending in said givendirection.
 11. The control device of claim 10 wherein said permanentmagnets comprise axially polarized circular discs mounted in generallyaxially opposed relation adjacent opposIte ends of said bellows chamber.12. The control device of claim 11 wherein said magnets comprise ceramicdisc magnets mounted in coaxially opposed relation adjacent oppositeends of said flexible bellows.
 13. The control device of claim 12wherein said disc permanent magnets are mounted one on each of said endcaps in generally axially opposed relation with the one pole of one ofsaid magnets facing the opposite pole of the other of said magnets.